Dissolved iron:phosphate ratio as an indicator of phosphate release to oxic water of the inner and outer coastal Baltic Sea: Part I: Sediment-Water Interaction 13 (Guest Editor: H.L. Golterman) Part II: Salt Ecosystems Section (Guest Editors: John M. Melack & Patrick Sorgeloos)

Author： Lehtoranta Jouni Heiskanen Anna-Stiina

Publisher： Springer Publishing Company

ISSN： 0018-8158

Source： Hydrobiologia, Vol.492, Iss.1-3, 2003-02, pp. : 69-84

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Abstract

Pore water concentrations and benthic fluxes of dissolved Fe, P and N were measured at two coastal basins in the Gulf of Finland, northern Baltic Sea, during a seasonal cycle. The bioturbated inner coastal basin, where exchange of near-bottom water is efficient, had a better ability to retain P in sediments than the outer basin, where near-bottom water O₂ concentration decreases during summer. Under the presence of O₂ high pore water dissolved Fe:P ratio (>3.6 w:w) in surface layer of the sediment, measured especially in winter, indicated negligible or low P-release and high N:P ratio in the efflux. On the contrary, low Fe:P ratio (<3.6), measured in summer and autumn, indicated high efflux of P and low N:P flux ratio. The low dissolved Fe:P ratio suggested that there was not enough diffusing Fe to form Fe³⁺ oxide-rich layer in the oxic surface zone of the sediments or near-bottom water to bind the P diffusing from the sediment. However, in sediments bioturbated by the abundant bivalve Macoma baltica, small efflux of P were measured almost throughout the study period. Thus, the Fe:P ratio cannot alone explain the P-release in bioturbated sediments. The low N:P ratio in the efflux measured in summer and autumn partly explains the measured low N:P ratio in the near-bottom water and thus N limitation of primary production in the Gulf. Additionally, it is evident that the release of P in the Gulf itself is of great importance for the trophic state of the Gulf of Finland.